1. Field of the Invention
The present invention relates to an optical semiconductor device in which a light emitting element and a light receiving photo-electric conversion element for monitoring light from said light emitting element are mounted integrally.
2. Description of the Prior Art
FIG. 1 is a cross sectional view of a conventional semiconductor light receiving photo-electric conversion element having a planar structure. In FIG. 1, the semiconductor light receiving photo-electric conversion element 14 is formed of a N type semiconductor substrate 1, a p type semiconductor layer 2 formed by diffusion, etc. on the substrate 1, an insulating layer 3, a p side electrode 4 and a n side electrode 5.
FIG. 2 shows a conventional optical semiconductor device in which a semiconductor light emitting element and a semiconductor light receiving photo-electric conversion element for monitoring and feeding back the optical output from the light emitting element are mounted on the same package. In FIG. 2, the conventional optical semiconductor device comprises a light emitting element 11, a block 13 for fixing the light emitting element 11, a light receiving photo-electric conversion element 14, a mount base 18 for mounting the light receiving element 14, a package 15, a lead terminal 16 and a lead wire 17. As shown in FIG. 2, the light receiving element 14 is mounted at an inclination to the light from the light emitting element. This is to prevent the reflected light at the light receiving portion from returning to the light emitting element, since the returned light derived from the reflection at the light receiving surface of the light receiving element 14 significantly affects the characteristics of the light emitting element 11. A semiconductor laser device devised to prevent the bad influence of the reflected light is disclosed in, for example, Patent Publication Gazette No. 1914/1982, in which a photodiode is mounted at an angle of 8.degree. to 10.degree. with the incident light in order that the light irradiated from the laser light emitting element to the monitoring photodiode may not be reflected to the light emitting element to affect badly.
The operation of the conventional optical semiconductor device shown in FIGS. 1 and 2 will be hereinafter described. As shown in FIG. 2, the light 12a emitted from a rear surface of the light emitting element 11 enters the p type semiconductor layer 2 of the light receiving surface of the light receiving element 14. The incident light is absorbed in each of the layers to generate hole.multidot.electron pairs. On this occasion, with a reverse bias applied between the p side electrode 4 and the n side electrode 5, a depletion layer extends at the pn junction interface to generate an electric field, so that the hole.multidot.electron pairs move along the electric field and flow to the lead terminal 16 as an optical current.
As shown in FIG. 2, in a conventional optical semiconductor device, the light receiving element 14 must be mounted at an inclination. Therefore, the conventional device presents problems that it must be provided with an inclined mount base 18, that the efficiency of photo-electric conversion lowers and that the work of assembly is troublesome.